308 PRACTICAL BOTANY 



epidermal cells contain chlorophyll : there are no 

 stomata. 



2. The mesophyll consists in its upper part of 

 thin -walled cells containing chlorophyll, and with small 

 intercellular spaces; this passes by gradual transition 

 into the lower part, where the intercellular spaces are 

 larger, and the form of the cells less regular. Internal 

 glandular hairs are frequently to be found in the inter- 

 cellular spaces of the mesophyll. 



3. The lower epidermis, the cells of which also 

 contain chlorophyll : numerous stomata are present : 

 note the form of the two guard-cells as seen in 

 transverse section, and their position in relation to 

 the epidermis. 



4. Here and there vascular bundles, of circular 

 appearance in transverse section, will be found em- 

 bedded in the mesophyll : the larger of these correspond 

 in position to the swollen ribs of the pinna. 



Note the endodermis as a continuous layer of 

 cells, which completely surrounds the circular bundle, 

 and within this the xylem and phloem elements, similar 

 to those of the stem : the bundles show a tendency to 

 the collateral type, the xylem being nearest to the 

 upper surface of the leaf. 



XVII. Cut tangential sections (or strip off the epider- 

 mis) from the upper and the lower surface of the leaf : 

 mount as before, and compare them. 



a. The epidermis of the upper surface will be 

 found to consist of cells with sinuous outline, and 

 protoplasmic contents, with chlorophyll : no stomata 

 will be found. 



I. The epidermis of the lower surface consists of 



